Resolution enhancement for macro wafer inspection

Abstract

A method and apparatus for improving system resolution for a defect line scanner while not increasing aliasing effects, or alternatively to maintain system resolution for a defect scanner while decreasing aliasing effects. This is accomplished by decreasing effective pixel size for a CCD array defect line scanner while not decreasing signal-to-noise ratio, with minimal changes to the current machine. The method utilizes a sampling phase shift between successive lines of a multi-line sensor array during scanning.

1. A line-scan wafer inspection system having the capability of forming an image of an illuminated wafer sample, said wafer inspection system including:
 a line imaging system and associated optics; 
 said imaging system including a scanner sensor array for optically sampling outgoing light from said sample surface, said scanner sensor array comprising a plurality of coplanar linear sensor arrays in a focal plane, each said linear sensor array arranged perpendicular to a scan direction of said scanner sensor array relative to said sample, each said linear sensor array comprising abutting optical sensors, each said sensor being a pixel having a pixel width, each said linear sensor array having an actual linear pixel density, wherein; 
 said scanner sensor array is arranged to provide a shift in sampling in adjacent linear sensor arrays, wherein the sampling in at least a portion of said linear sensor arrays is shifted by a fraction of a pixel width with respect to adjacent linear sensor arrays, to provide optical sampling data from said sample which yields an effective linear pixel density greater than said actual linear pixel density; 
 wherein said shift in sampling in adjacent linear sensor arrays is provided by one selected from the group consisting of: 
 a) said scanner sensor array being rotated in said focal plane by an angle θ with respect to said scan direction; and 
 b) a first portion of each pixel being masked and a second portion of each pixel being unmasked, wherein said second portion is shifted in each successive linear sensor array, such that the sampling is performed at progressively offset locations. 
 
   
   
     2. The wafer inspection system of  claim 1 , wherein said associated optics includes a lens between said sample and said sample sensor array. 
   
   
     3. The wafer inspection system of  claim 2 , further including an aperture for stopping said lens. 
   
   
     4. The wafer inspection system of  claim 1 , wherein said associated optics provide magnification to provide for micro-inspection. 
   
   
     5. The wafer inspection system of  claim 1 , wherein said imaging system includes non-standard elements. 
   
   
     6. The wafer inspection system of  claim 1 , wherein said imaging system includes gradient index lenses. 
   
   
     7. The wafer inspection system of  claim 1 , wherein said sampling in at least a portion of adjacent linear sensor arrays is partially overlapping in corresponding pixels of said adjacent linear sensor arrays, such that said effective linear pixel density greater than said actual linear pixel density is provided by deconvolving data from said partially overlapping sampling. 
   
   
     8. The wafer inspection system of  claim 7 , further including a computer system configured to process said data from said partially overlapping sampling so as to deconvolve said data. 
   
   
     9. The wafer inspection system of  claim 1 , wherein said scanner sensor array is rotated in said focal plane by an angle θ with respect to said scan direction to provide said shift in sampling in adjacent linear sensor arrays. 
   
   
     10. The wafer inspection system of  claim 9 , wherein said scanner sensor array comprises n linear sensor arrays, and wherein said angle θ with respect to said scan direction is chosen such that said shift in sampling in adjacent linear sensor arrays is 1/n pixels. 
   
   
     11. The wafer inspection system of  claim 10 , wherein n=3. 
   
   
     12. The method of  claim 10 , wherein said angle θ is no larger than on the order of 1.6 degrees. 
   
   
     13. The wafer inspection system of  claim 1 ,
 where a first portion of each pixel is masked and a second portion of each pixel is unmasked, wherein said second portion is shifted in each successive linear sensor array, such that the sampling is performed at progressively offset locations to provide said shift in sampling in adjacent linear sensor arrays. 
 
   
   
     14. The wafer inspection system of  claim 13 , wherein said scanner sensor array comprises n linear sensor arrays, and wherein said shift of said second portion in each successive linear sensor array is 1/n pixels. 
   
   
     15. A method for increasing effective pixel resolution in a line-scan wafer inspection system including a scanner sensor array comprising a plurality of coplanar linear sensor arrays in a focal plane, each said linear sensor array comprising abutting sensors, each said sensor being a pixel having a pixel width, the method comprising:
 providing said scanner sensor array, arranged to sample outgoing light from the surface of said wafer sample, such that the sampling in at least a portion of adjacent linear sensor arrays is shifted by a fraction of a pixel; 
 providing a wafer sample to be imaged; 
 providing a line imaging system and associated optics; 
 causing relative motion in a scan direction between said scanner sensor array and said wafer sample, said wafer sample being illuminated; 
 sampling outgoing light from said wafer sample with said scanner sensor array, each said sensor of one pixel width yielding an electrical signal; and 
 processing said electrical signals from said sensors of one pixel width to form an image of said wafers; 
 wherein the step of providing said scanner sensor array arranged to sample outgoing light from the surface of said wafer sample such that the sampling in at least a portion of adjacent linear sensor arrays is shifted by a fraction of a pixel is performed by one of the group consisting of: 
 a) arranging said scanner sensor array to be rotated in said focal plane by an angle θ such that said coplanar linear sensor arrays are arranged at said angle θ with respect to the perpendicular to the scan direction; and 
 b) arranging said scanner sensor array such that a first portion of each pixel is masked and a second portion of each pixel is unmasked, wherein said second portion is shifted in each successive linear sensor array, such that the sampling is performed at progressively offset locations. 
 
   
   
     16. The method of  claim 15 , further including the step of deconvolving overlapping sampling data from corresponding pixels in adjacent linear sensor arrays. 
   
   
     17. The method of  claim 15 , wherein the step of providing said scanner sensor array arranged to sample outgoing light from the surface of said wafer sample such that the sampling in at least a portion of adjacent linear sensor arrays is shifted by a fraction of a pixel includes arranging said scanner sensor array to be rotated in said focal plane by an angle θ such that said coplanar linear sensor arrays are arranged at said angle θ with respect to the perpendicular to the scan direction. 
   
   
     18. The method of  claim 17 , wherein said angle θ is no larger than on the order of 1.6 degrees. 
   
   
     19. The method of  claim 15 , wherein the step of providing said scanner sensor array, arranged to sample outgoing light from the surface of said wafer sample, such that the sampling in at least a portion of adjacent linear sensor arrays is shifted by a fraction of a pixel includes arranging said scanner sensor array such that a first portion of each pixel is masked and a second portion of each pixel is unmasked, wherein said second portion is shifted in each successive linear sensor array, such that the sampling is performed at progressively offset locations.